It's original definition was "Laughing out loud" (also written occasionally as "Lots of Laughs"), used as a brief acronym to denote great amusement in chat conversations.

Now, it is overused to the point where nobody laughs out loud when they say it. In fact, they probably don't even give a shit about what you just wrote. More accurately, the acronym "lol" should be redefined as "Lack of laughter."

Depending on the chatter, its definition may vary. The list of its meanings includes, but is not limited to:
1) "I have nothing worthwhile to contribute to this conversation."
2) "I'm too lazy to read what you just wrote so I'm typing something useless in hopes that you'll think I'm still paying attention."
3) "Your statement lacks even the vaguest trace of humor but I'll pretend I'm amused."
4) "This is a pointless acronym I'm sticking in my sentence just because it's become so engraved into my mind that when chatting, I MUST use the meaningless sentence-filler 'lol.'"

lol - originally meant "laughing out loud", but now is the most common expression in any text conversation, just used instead of HAHA or any giggle or something like that. Also used all the time when there's nothing else to say... LOL key should be added to a standard keyboard.

It stands for "laughing out loud." A slight irony to this definition is that generally people don't literally laugh out loud. That's reserved for other acronyms such as, but not limited to, LMMFAO, LMAO, ROTFLMAO, etc. Lol is most commonly used as a slience breaker, a reply to a joke that is SUPPOSED to be funny but really isn't, or an answer to an uncomfortable or random statement that one couldn't think of a better response to.

Originally meant "laughing out loud" but is now so overused that it now means "I find that vaguely amusing" also a filler word now when there is a puse in the conversation or the person is lost for a response, or they are too stupid or lazy to think of one.